In most countries, sleeping on the job isn't just frowned upon, it may get you fired.

But in Japan, napping in the office is common and culturally accepted. And in fact, it is often seen as a subtle sign of diligence: You must be working yourself to exhaustion.

The word for it is "inemuri". It is often translated as "sleeping on duty," but Dr Brigitte Steger, a senior lecturer in Japanese studies at Downing College, Cambridge, who has written a book on the topic, says it would be more accurate to render it as "sleeping while present".

That, she said, captures Japan's approach to time, where it's seen as possible to do multiple things simultaneously, if at a lower intensity. So you can get credit for attending that boring quarterly sales meeting while also dreaming of a beach vacation.

Inemuri is most prevalent among more senior employees in white-collar professions, Dr Steger said. Junior employees tend to want to stay awake all day and be seen as energetic, and workers on assembly lines can't just nod off.

Both sexes indulge in inemuri, but women are more likely to be criticised for it, especially if they sleep in a position that is considered unbecoming, Dr Steger said.

Inemuri has been practiced in Japan for at least 1000 years, and it is not restricted to the workplace. People may nap in department stores, cafes, restaurants or even a snug spot on a busy city sidewalk.

Sleeping in public is especially prevalent on commuter trains, no matter how crowded; they often turn into de facto bedrooms. It helps that Japan has a very low crime rate.

"It's very unlikely, if you are sleeping on a train, that someone would try to rob you," said Theodore C. Bestor, a professor of social anthropology at Harvard University.

Sleeping in social situations can even enhance your reputation. Dr Steger recalled a group dinner at a restaurant where the male guest of a female colleague fell asleep at the table. The other guests complimented his "gentlemanly behaviour" that he chose to stay present and sleep, rather than excuse himself.

One reason public sleeping may be so common in Japan is because people get so little sleep at home. A 2015 government study found that 39.5 per cent of Japanese adults slept less than six hours a night.

An unwritten rule of inemuri is to sleep compactly, without "violating spatial norms," Bestor said. "If you stretched out under the table in the office conference room, or took up several spaces on the train, or laid out on a park bench," he said, that would draw reproach for being socially disruptive.

Dr Steger pointed out that closed eyes may not always equal shut-eye: A person may close them just to build a sphere of privacy in a society with little of it.

That's part of why Dr Steger said she could imagine inemuri waning in Japan. These days, smartphones can transport people to their own private zones with their eyes wide open.

The New York Times